Dear L:

You wrote:

> My question is which version is correct and why.
>
> 1. To whom it may concern
> or
> 2. To who it may concern
>
“To whom it may concern” is correct.

“Whom” is the Objective Case; just like “him” and “them” it ends with an “m.” It serves as an object– direct object, indirect object, or object of a preposition. Here it is the object of the preposition “to.” In the same way we say “to him” rather than “to he” or “to them” rather than “to they,” we say “to whom” rather than “to who.” A teacher once said that “to who” is what an owl says, “to whom” is what an Englishman says.

Having said all that, back in 2001 Time magazine had an article which was trying to predict what kind of things would happen in the next century. One of the things it predicted was that whom would disappear from the language.